Conventionally, a centrifuge comprises:                a drive shaft;        a rotor intended to be removably mounted on the drive shaft in a mounting position in which the drive shaft and rotor are rotatably coupled;        a device for axially blocking the rotor on the drive shaft, comprising a male element carried by the rotor, resiliently biased and capable of occupying a cooperation position with an element presented by the drive shaft.        
Such a centrifuge also comprises motor means intended to drive the drive shaft of the rotor in rotation, these motor means being connected to power supply means controlled by an operator-actuable command to launch a centrifugation cycle.
During the design, production and utilization of such a centrifuge, one of the parameters essential for the proper operation of a centrifuge, which must be carefully considered, relates to the balancing of rotating parts. In fact, centrifuges are machines capable of rotating at very high speeds (up to 150,000 rotations/min. for ultracentrifuges) and ensuring the proper balancing of the machine is indispensable for preventing the machine from producing, during operation, vibrations beyond a certain amplitude. In fact, these vibrations greatly disturb the centrifugation quality since they re-suspend products that were previously separated. In addition, these vibrations cause premature aging of the rotation system and suspension means. This aging may lead to breakage of parts and to an accident involving the operator.
Balancing consists of uniformly distributing the weight of the parts on the rotor, around the axis of revolution of the rotor. Currently, the balancing of parts to eliminate imbalances is done by hand. The operators, depending on their experience, quickly adjust the position of the parts to ensure optimal and safe centrifugation with varying degrees of success.
An additional difficulty resides in the fact that certain rotation speeds cause the rotation system to resonate and increases the vibrations applied to the products to be centrifuged. Experiments show that the resonance speed intervenes for a rotation speed well below the set speed, such that resonance intervenes both during acceleration and during braking Centrifuges are mainly used today to separate blood components. The separation takes, for example, 30 minutes and is carried out at a speed of 10,000 rotations per minute. If resonance generating significant vibrations intervenes during the braking phase, the blood components (platelets, white blood cells, red blood cells) will be mixed together again. A defect in the separation of components is catastrophic since this type of operation cannot be repeated and because of this, the blood bags must be discarded.
Document US 2010/0069216 A1 describes a method for controlling a centrifuge comprising a shaft coupled to a rotor, and a balancer that comprises an annular space in which a compensating material in the form of bead enables the samples to be centrifuged to be balanced. These beads freely displace in the annular space. The control comprises acceleration of the rotor beyond the resonance speed to achieve balancing, the measurement of vibrations, and the determination of the possibility or impossibility to accelerate and then decelerate below the resonance speed. However, this bead balancer presents the disadvantage that at the end of a centrifugation cycle, the beads will not necessarily return to their initial position, thus causing an additional imbalance.
Document EP 1 247 585 describes a balancing system for washing machines or medical-use centrifuges comprising two plates integral with a drive shaft, between which two rings surround said shaft. When stopped, a spring placed between one of the plates and a disk maintains the rings blocked. In operation, when the centrifugation speed reaches a certain value, oscillating bodies in contact with the disk pivot, thereby releasing the rings. When the centrifuge slows down, the rings are again blocked in their last position. However, the last ring position thus obtained corresponds to the centrifuge loading in progress. During a new loading, the blocking of rings in a particular position risks increasing the centrifuge imbalance, such that the balancing system will not eliminate the imbalance.